In order to minimize maintenance and provide satisfactory operation over extended periods for high pressure valves as well as valves used in particular environments and/or with particular fluids, it is desirable to utilize metal-to-metal sealing rather than an elastomer or the like. It is further desirable that valves operated in high pressures or other severe environments be relatively easy to repair and be of a so-called unitized construction so that the interior parts of the vavle can be removed as a unit for easy replacement and/or repair.